Wireless communication terminal and wireless communication method for multi-user concurrent transmission

ABSTRACT

The present invention relates to a wireless communication terminal and a wireless communication method for efficiently managing simultaneous data transmissions of a plurality of terminals.To this end, provided are a base wireless communication terminal including: a transceiver configured to transmit and receive a wireless signal; and a processor configured to control an operation of the base wireless communication terminal, wherein the processor is configured to: transmit a trigger frame triggering a multi-user uplink transmission of a plurality of terminals, receive multi-user uplink data through resources allocated to the plurality of terminals, and transmit a block ACK through the resources in response to the received multi-user uplink data, wherein the transmission of the block ACK in each resource is terminated at the same time, and a wireless communication method using the same.

TECHNICAL FIELD

The present invention relates to a wireless communication terminal and awireless communication method for a simultaneous multi-usertransmission, and more particularly, to a wireless communicationterminal and a wireless communication method for efficiently managingsimultaneous data transmissions of a plurality of terminals.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

The present invention has an object to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment as described above.

In addition, the present invention has an object to reduce thepossibility of collision of data transmission of a plurality ofterminals in a dense user environment and to provide a stable datacommunication environment.

Also, the present invention has an object to provide a method by which aplurality of terminals can efficiently perform simultaneous multi-usertransmission.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, an exemplary embodiment of the present invention provides a basewireless communication terminal, including: a transceiver configured totransmit and receive a wireless signal; and a processor configured tocontrol an operation of the base wireless communication terminal,wherein the processor transmits a trigger frame triggering a multi-useruplink transmission of a plurality of terminals, receives multi-useruplink data through resources allocated to the plurality of terminals,and transmits a block ACK through the resources in response to thereceived multi-user uplink data, wherein the transmission of the blockACK in each resource is terminated at the same time.

According to an embodiment, the processor may perform padding on theblock ACK transmitted through at least one resource to match terminationpoints of block ACK transmissions in each resource.

According to another embodiment, the processor may insert duplicated ACKinformation into the block ACK transmitted through at least one resourceto match termination points of block ACK transmissions in each resource.

In addition, a predetermined padding may be performed before a framecheck sequence (FCS) field of the trigger frame.

In this case, the transmission of the trigger frame may be terminated atthe same time in each resource through which the trigger frame istransmitted.

In addition, the resource may be a channel or a sub-channel.

According to an embodiment, a transmission packet of the multi-useruplink data may include a legacy preamble and a non-legacy preamble, andthe legacy preamble may be received as common information on a 20 MHzchannel basis.

In addition, the non-legacy preamble may include HE-SIG-A and remainingfields, and the HE-SIG-A may be received as common information on a 20MHz channel basis, and the remaining fields of the non-legacy preamblesmay be received as individual information for each resource allocated toeach terminal.

In this case, the remaining fields of the non-legacy preamble mayinclude HE-STF and HE-LTF.

According to an embodiment, the multi-user uplink data transmission ineach resource may be terminated at the same time.

In this case, the uplink data transmitted through at least one resourcemay be padded to terminate the multi-user uplink data transmission atthe same time.

In addition, an exemplary embodiment of the present invention provides awireless communication method of a base wireless communication terminal,including: transmitting a trigger frame triggering a multi-user uplinktransmission of a plurality of terminals; receiving multi-user uplinkdata through resources allocated to the plurality of terminals; andtransmitting a block ACK through the resources in response to thereceived multi-user uplink data; wherein the transmission of the blockACK in each resource is terminated at the same time.

Advantageous Effects

According to an embodiment of the present invention, efficientmulti-user uplink transmission scheduling is possible in acontention-based channel access system.

Also, according to the embodiment of the present invention, it ispossible to reduce unnecessary channel occupancy and increase totalspectral efficiency of the network in a multi-user uplink transmissionprocess.

In addition, according to the embodiment of the present invention, it ispossible to prevent malfunction of the wireless LAN network by aligningthe lengths of block ACKs transmitted through a plurality of channels,and at the same time, it is possible to secure transmission time of acontrol frame of an AP.

According to the embodiment of the present invention, it is possible toincrease the total resource utilization rate in the contention-basedchannel access system and improve the performance of the wireless LANsystem.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a wireless LAN system according to an embodiment ofthe present invention.

FIG. 2 illustrates a wireless LAN system according to another embodimentof the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 schematically illustrates a process in which a STA and an AP seta link.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

FIG. 7 illustrates a method for performing a distributed coordinationfunction (DCF) using a request to send (RTS) frame and a clear to send(CTS) frame.

FIG. 8 illustrates a wireless LAN network according to an embodiment ofthe present invention.

FIG. 9 illustrates a sequence of processes in which a multi-user uplinktransmission is performed according to an embodiment of the presentinvention.

FIG. 10 illustrates an ACK transmission method for a multi-user uplinktransmission according to an embodiment of the present invention.

FIG. 11 illustrates a NAV setting method for a multi-user uplinktransmission according to an embodiment of the present invention.

FIG. 12 illustrates a frequency masking method according to thefrequency bandwidth in use.

FIG. 13 illustrates a guard band setting method according to anembodiment of the present invention.

FIG. 14 illustrates a method of transmitting a legacy preamble of anon-legacy terminal in a process of a multi-user uplink datatransmission.

FIG. 15 illustrates a method of configuring a non-legacy preamble in aprocess of a multi-user data transmission.

FIG. 16 illustrates a method for performing a multi-user uplinktransmission according to an embodiment of the present invention.

FIG. 17 illustrates a structure of a multiplexed group ACK according toan embodiment of the present invention.

FIG. 18 illustrates a method of transmitting a multiplexed group ACKaccording to an embodiment of the present invention.

FIG. 19 illustrates a length alignment method of block ACKs according toan embodiment of the present invention.

FIG. 20 illustrates a method of frame length alignment by padding in amulti-user simultaneous transmission according to an embodiment of thepresent invention.

FIG. 21 illustrates a method of transmitting a multiplexed block ACKwhen a plurality of channels are used for a multi-user uplinktransmission.

BEST MODE

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2015-0030369, 10-2015-0036754 and 10-2015-0066670filed in the Korean Intellectual Property Office and the embodiments andmentioned items described in the respective application, which forms thebasis of the priority, shall be included in the Detailed Description ofthe present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1 , the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a transceiver andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the transceiver is functionally connected withthe processor and transmits and receives frames through the wirelessnetwork for the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense. In the present invention, an AP may also be referredto as a base wireless communication terminal. The base wirelesscommunication terminal may be used as a term which includes an AP, abase station, an eNB (i.e. eNodeB) and a transmission point (TP) in abroad sense. In addition, the base wireless communication terminal mayinclude various types of wireless communication terminals that allocatemedium resources and perform scheduling in communication with aplurality of wireless communication terminals.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2 , duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1 , will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3 , the station 100 according to the embodimentof the present invention may include a processor 110, a transceiver 120,a user interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 controls various operations of wirelesssignal transmission/reception of the station 100 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4 , the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4 , among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4 , the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3 , thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 controls variousoperations such as wireless signal transmission/reception of the AP 200according to the embodiment of the present invention. A detailedembodiment thereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5 , the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b). In this specification, an association basically means awireless association, but the present invention is not limited thereto,and the association may include both the wireless association and awired association in a broad sense.

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5 , the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

FIG. 6 is a diagram illustrating a carrier sense multiple access(CSMA)/collision avoidance (CA) method used in wireless LANcommunication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a wireless signal having a predetermined strength or more issensed, it is determined that the corresponding channel is busy and theterminal delays the access to the corresponding channel. Such a processis referred to as clear channel assessment (CCA) and a level to decidewhether the corresponding signal is sensed is referred to as a CCAthreshold. When a wireless signal having the CCA threshold or more,which is received by the terminal, indicates the corresponding terminalas a receiver, the terminal processes the received wireless signal.Meanwhile, when a wireless signal is not sensed in the correspondingchannel or a wireless signal having a strength smaller than the CCAthreshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an interframespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber assigned to the corresponding terminal during an interval of anidle state of the channel and a terminal that completely exhausts theslot time(s) attempts to access the corresponding channel. As such, aninterval in which each terminal performs the backoff procedure isreferred to as a contention window interval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the access collides with anotherterminal, the terminals which collide with each other are assigned withnew random numbers, respectively to perform the backoff procedure again.According to an embodiment, a random number newly assigned to eachterminal may be decided within a range (2*CW) which is twice larger thana range (a contention window, CW) of a random number which thecorresponding terminal is previously assigned. Meanwhile, each terminalattempts the access by performing the backoff procedure again in a nextcontention window interval and in this case, each terminal performs thebackoff procedure from slot time(s) which remained in the previouscontention window interval. By such a method, the respective terminalsthat perform the wireless LAN communication may avoid a mutual collisionfor a specific channel.

FIG. 7 is a diagram illustrating a method for performing a distributedcoordination function using a request to send (RTS) frame and a clear tosend (CTS) frame.

The AP and STAs in the BSS contend in order to obtain an authority fortransmitting data. When data transmission at the previous step iscompleted, each terminal having data to be transmitted performs abackoff procedure while decreasing a backoff counter (alternatively, abackoff timer) of a random number allocated to each terminal after anAFIS time. A transmitting terminal in which the backoff counter expirestransmits the request to send (RTS) frame to notify that correspondingterminal has data to transmit. According to an exemplary embodiment ofFIG. 7 , STA1 which holds a lead in contention with minimum backoff maytransmit the RTS frame after the backoff counter expires. The RTS frameincludes information on a receiver address, a transmitter address, andduration. A receiving terminal (i.e., the AP in FIG. 7 ) that receivesthe RTS frame transmits the clear to send (CTS) frame after waiting fora short IFS (SIFS) time to notify that the data transmission isavailable to the transmitting terminal STA1. The CTS frame includes theinformation on a receiver address and duration. In this case, thereceiver address of the CTS frame may be set identically to atransmitter address of the RTS frame corresponding thereto, that is, anaddress of the transmitting terminal STA1.

The transmitting terminal STA1 that receives the CTS frame transmits thedata after a SIFS time. When the data transmission is completed, thereceiving terminal AP transmits an acknowledgment (ACK) frame after aSIFS time to notify that the data transmission is completed. When thetransmitting terminal receives the ACK frame within a predeterminedtime, the transmitting terminal regards that the data transmission issuccessful. However, when the transmitting terminal does not receive theACK frame within the predetermined time, the transmitting terminalregards that the data transmission is failed. Meanwhile, adjacentterminals that receive at least one of the RTS frame and the CTS framein the course of the transmission procedure set a network allocationvector (NAV) and do not perform data transmission until the set NAV isterminated. In this case, the NAV of each terminal may be set based on aduration field of the received RTS frame or CTS frame.

In the course of the aforementioned data transmission procedure, whenthe RTS frame or CTS frame of the terminals is not normally transferredto a target terminal (i.e., a terminal of the receiver address) due to asituation such as interference or a collision, a subsequent process issuspended. The transmitting terminal STA1 that transmitted the RTS frameregards that the data transmission is unavailable and participates in anext contention by being allocated with a new random number. In thiscase, the newly allocated random number may be determined within a range(2*CW) twice larger than a previous predetermined random number range (acontention window, CW).

Multi-User Uplink Transmission

FIG. 8 illustrates a wireless LAN network according to an embodiment ofthe present invention. In FIG. 8 , a BSS consists of an AP and aplurality of STAs (STA1, STA2, STA3 and STA4) associated therewith. Theblocks shown with each terminal represents the channel state measured atthe corresponding terminal. A shadow block indicates a busy channel, anda white block indicates an idle channel.

When using an orthogonal frequency division multiple access (OFDMA) or amulti-input multi-output (MIMO), one wireless communication terminal cansimultaneously transmit data to a plurality of wireless communicationterminals. Further, one wireless communication terminal cansimultaneously receive data from a plurality of wireless communicationterminals. For example, a multi-user downlink transmission in which anAP simultaneously transmits data to a plurality of STAs, and amulti-user uplink transmission in which a plurality of STAssimultaneously transmit data to the AP may be performed.

In order to perform the multi-user uplink transmission, the channel tobe used and the transmission start time of each STA that performs uplinktransmission should be adjusted. However, in a wireless LAN environmentin which a plurality of BSSs are adjacent to each other, the measuredchannel states may be different from each other in the same BSS as shownin FIG. 8 . That is, depending on the influence of the adjacent externalBSS of each terminal, channels to which each terminal can access may bedifferent from each other. In addition, whether or not each STA has datafor uplink transmission changes in real time. Therefore, in order toefficiently schedule the multi-user uplink transmission, stateinformation of each STA needs to be transmitted to the AP.

According to an embodiment of the present invention, information forscheduling of a multi-user uplink transmission may be indicated througha predetermined field of a preamble of a packet and/or a predeterminedfield of a MAC header. For example, a STA may indicate information formulti-user uplink transmission scheduling through a predetermined fieldof a preamble or a MAC header of an uplink transmission packet, and maytransmit the information to an AP. In this case, the information formulti-user uplink transmission scheduling includes at least one ofbuffer status information of each STA, channel state informationmeasured by each STA. The buffer status information of the STA mayindicate at least one of whether the STA has uplink data to betransmitted, the access class (AC) of the uplink data and the size (orthe transmission time) of the uplink data.

FIG. 9 illustrates a sequence of processes in which a multi-user uplinktransmission is performed. As described above, the multi-user uplinktransmission process may be managed by the AP because a plurality ofterminals simultaneously transmit data. Therefore, in order to allocateresources and prevent data collision, the AP should obtain the bufferstatus information of each STA and deliver the accurate transmissiontime point information to each STA before the start of multi-user uplinktransmission. The buffer status information of the STA may indicate atleast one of whether the STA has uplink data to be transmitted, theaccess category (AC) of the uplink data, and the size (or thetransmission time) of the uplink data. Such information delivery of eachSTA may be performed through an initialization step S210 and ascheduling step S220 for the multi-user uplink transmission.

According to an embodiment of the present invention, the scheduling stepS220 for the multi-user uplink transmission is performed in advance tocollect related information, and the initialization step S210 may beperformed if a specific condition is satisfied. Alternatively, theinitialization step S210 may be performed in advance according to thetime condition, and then the scheduling step S220 may be performed nextto collect the related information. The initializing step S210 and thescheduling step S220 include a process of exchanging information onchannels available to the AP and the STA. According to an exemplaryembodiment, the AP may transmit available channel information to aplurality of STAs in advance, and the plurality of STAs may feedbackchannel information available to the corresponding STA among thechannels available to the AP. The specific operation method of theinitializing step S210 and the scheduling step S220 in the embodiment ofthe present invention is not limited thereto. According to anembodiment, the initialization step S210 and the scheduling step S220may be performed with an integrated operation.

When the initialization step S210 and the scheduling step S220 areperformed, a multi-user uplink data transmission step S230 is performed.At least one STA assigned a channel or a sub-channel from the APsimultaneously transmits uplink data at the time point designated by theAP. The STA may perform uplink data transmission through a 20 MHzchannel basis or a wideband channel basis over the 20 MHz. In addition,the non-legacy STA may perform uplink data transmission through asub-channel basis smaller than 20 MHz. In the embodiment of the presentinvention, a term resource may be used for comprehensively meaning achannel or a sub-channel allocated to the STAs. The AP receiving theuplink data from the STA transmits an ACK in response thereto (S240). Ifuplink data transmission is performed through a sub-channel basis, aplurality of STAs can transmit uplink data through one channel. In thiscase, the AP may transmit a group ACK through the corresponding channelto transmit an ACK for a plurality of STAs that transmitted the uplinkdata.

In case of being affected by a plurality of external BSSs in a dense BSSenvironment, the available channels of each terminal may be differentfrom each other according to the geographical location of the wirelessterminal. Therefore, the number of terminals capable of datatransmission through each channel may be different from each other. Inthis case, as shown in FIG. 9 , the air time during which actual uplinkdata transmission is performed may be different for each channel.However, if the AP cannot simultaneously perform data transmission andreception, the AP cannot transmit an ACK through another channel inwhich uplink data transmission has been completed while receiving uplinkdata through a channel in which the air time is long. Therefore, theSTAs using the channel in which the air time is short may perform zeropadding until the uplink data transmission of a channel having thelongest air time is completed, to wait for ACK reception (S250). Thatis, the padding is performed on the uplink data transmitted through atleast one channel, so that the multi-user uplink data transmission ineach channel can be terminated at the same time.

However, when the zero padding is performed, STAs occupy the channelregardless of data transmission, thus the overall spectral efficiency islowered. In addition, terminals of other BSSs using the channel as aprimary channel cannot perform communication during the zero paddingperiod, and thus directly experience a decrease in performance.Therefore, there is a need for an ACK transmission method for furtherimproving the data transmission efficiency of the terminals.

FIG. 10 illustrates an ACK transmission method for multi-user uplinktransmission according to an embodiment of the present invention. Whenthe multi-user uplink transmission is completed, the AP transmits amultiplexed group ACK in response thereto (S244). In this case, the APmay transmit the multiplexed group ACK through a first channel havingthe longest air time among the plurality of channels in which themulti-user uplink transmission is performed. According to an embodiment,the first channel having the longest air time may be the primary channelof the BSS.

The STAs in which a channel other than the first channel is assigned asthe uplink data transmission channel set an ACK timer at the time whenthe uplink data transmission of the corresponding channel ends, and waitfor ACK reception until the set ACK timer expires (S242). In this case,the other channel may be a channel other than the first channel havingthe longest air time, that is, a secondary channel of the correspondingBSS. The ACK timer of each channel indicates the time from when theuplink data transmission of the corresponding channel is completed towhen the multiplexed group ACK is transmitted. For the setting of theACK timer, each STA should obtain information on the transmission timepoint of the multiplexed group ACK. The transmission time pointinformation of the multiplexed group ACK may be transmitted to each STAwhich is intended to perform uplink data transmission in theinitialization step S210 and/or the scheduling step S220. According toan exemplary embodiment, the STA that the ACK timer is set may switch toa sleep mode until the corresponding timer expires to perform a powersaving.

As described above, according to the embodiment of the presentinvention, each secondary channel can be returned immediately after theuplink data transmission is completed. Therefore, the terminals of theexternal BSS using the corresponding secondary channel as a primarychannel may access the channel and transmit data at an earlier timepoint. Thus, the overall spectral efficiency of the network can beimproved.

FIG. 11 illustrates a NAV setting method for a multi-user uplinktransmission according to an embodiment of the present invention. In theembodiment of FIG. 11 , the same or corresponding parts as those of theembodiment of FIG. 10 described above will be omitted.

According to an embodiment of the present invention, in order to protectthe multi-user uplink transmission process, a NAV setting frame may betransmitted. First, the AP transmits the first NAV setting frame at thestart time of the multi-user uplink transmission (S310). The actualtransmission length of the multi-user uplink transmission may varydepending on the uplink transmission data length and the resourceallocation result of the STAs. Thus, the duration field value of thefirst NAV setting frame may be set to durations of the initializationstep and the scheduling step. The first NAV setting frame may be an RTSor CTS of a predetermined format. According to an embodiment, the firstNAV setting frame may be one of a predefined multi-user RTS,RTS-to-self, CTS-to-self and CTS-to-group.

When the resource allocation of each STA is completed in the schedulingstep, an air time in which uplink data transmission is performed foreach channel is calculated. Accordingly, second NAV setting frames aretransmitted for setting a NAV during a period in which the multi-useruplink transmission and the multiplexed group ACK transmission areperformed (S320). The second NAV setting frame may be simultaneouslytransmitted by a plurality of STAs in which resource is allocated andparticipate in the multi-user uplink data transmission. Alternatively, aplurality of STAs and an AP may simultaneously transmit the second NAVsetting frame. According to an embodiment, the second NAV setting framemay be configured in a CTS frame format. In this case, second NAVsetting frames simultaneously transmitted by a plurality of STAs and/orthe AP may be set to the same waveform.

The NAVs of the neighboring terminals are set based on the first NAVsetting frame and the second NAV setting frame transmitted as above(S330, S340). Since the second NAV setting frames having the samewaveform are simultaneously transmitted on a 20 MHz channel basis, theneighboring terminals including legacy terminals can receive the secondNAV setting frame and set a NAV. When the simultaneously transmittedsecond NAV setting frames have the same waveform for each channel, thesecond NAV setting frame may have duration information reflecting theair time of the corresponding channel. Accordingly, a terminal of anexternal BSS that has acquired the NAV information set on the specificchannel can access the corresponding channel immediately after the NAVtime has expired.

On the other hand, when the multiplexed group ACK is used as in theembodiment of FIG. 10 , STAs that have transmitted uplink data throughsecondary channels receive the multiplexed group ACK through the primarychannel. If the STAs set the NAV only for the secondary channel throughwhich the uplink data is transmitted, terminals of the external BSSadjacent to the STA may regard the primary channel as idle and performan access to the primary channel. In this case, STAs that have beentransmitted the uplink data through the secondary channels may not beable to receive the multiplexed group ACK transmitted through theprimary channel.

Therefore, according to the embodiment of the present invention, theSTAs transmitting uplink data through the secondary channel transmit thesecond NAV setting frame through the primary channel and the secondarychannel. In this case, the primary channel through which the second NAVsetting frame is transmitted is a primary channel of the BSS to whichthe corresponding STA belongs. In addition, the secondary channelthrough which the second NAV setting frame is transmitted is a secondarychannel through which the STA transmits uplink data. Referring to FIG.11 , STA4 and STA5 transmitting uplink data through a secondary channeltransmit a second NAV setting frame not only through the secondarychannel but also through a primary channel (S320). As described above,the STAs additionally protect the primary channel through which themultiplexed group ACK is transmitted as well as the secondary channelthrough which the uplink data is transmitted. The duration field valueof the second NAV setting frame transmitted through the primary channelis set to the time when the transmission of the multiplexed group ACK iscompleted. The duration field value of the second NAV setting frametransmitted through the secondary channel is set to the time when theuplink data transmission of the secondary channel is completed. On theother hand, STAT, STA2, and STA3 that transmit uplink data through theprimary channel are not required to transmit an additional second NAVsetting frame through channels other than the primary channel.

FIG. 12 illustrates a frequency masking method according to thefrequency bandwidth in use. In the wireless LAN system, a frequencymasking technique is used to minimize mutual interference when differentterminals perform communications through adjacent channels. Thefrequency masking is implemented in a way of intentionally reducingtransmission power at the boundary frequencies (i.e., the minimumfrequency and the maximum frequency) of the currently used channel.Therefore, the shape of frequency masking is different depending on thebandwidth in which data transmission is performed. That is, the spectralmask 410 of a packet transmitted on a 40 MHz channel has a differentshape from the spectral mask 420 of a packet transmitted on two adjacent20 MHz channels. In particular, each of the spectral masks 410 and 420has a difference in the presence or absence of the guard band 430 at thecentral frequency portion of the 40 MHz channel.

FIG. 13 illustrates a guard band setting method according to anembodiment of the present invention.

FIG. 13 (a) represents a situation where data 440 is transmitted onlythrough a channel of a second band after a specific time point from thetransmission of data 440 through a channel of a first band is started.In the embodiment of the present invention, the second band has anarrower bandwidth than the first band. For example, the first band mayrepresent a 40 MHz bandwidth, and the second band may represent a 20 MHzbandwidth. According to an embodiment of the present invention, thetransmission bandwidth may be changed during the transmission of data440 according to the scheduling of data transmission and the result ofresource allocation. Even if the transmission bandwidth is changed inthis manner, the spectral mask of the RF chain may be maintained in itsoriginal shape. That is, if the transmission band of the data is changedfrom the first hand to the second hand, data 440 in a form without theguard band 442 may be transmitted. In this case, when the terminal ofthe external BSS (i.e., OBSS) attempts to transmit on the idle band ofthe first hand, interference may occur due to absence of the guard band442 of data transmitted through the second band.

FIG. 13 (b) represents an embodiment in which data is transmitted bysetting a guard band 450 between two adjacent basic band channels.According to an embodiment of the present invention, when multi-userdata transmission is performed, data 440 a and 440 b allocated to eachterminal may be transmitted through bands below the basic band. In thiscase, the multi-user data transmission includes a multi-user uplink datatransmission and a multi-user downlink data transmission. Further, thebasic band may be a 20 MHz band, but the present invention is notlimited thereto. In this manner, the guard band 450 in units of thebasic band can be formed by setting a resource exceeding the basic bandas not to be allocated to a single terminal.

According to another embodiment of the present invention, when amulti-user data transmission is performed, data allocation of abroadband exceeding the basic band may be allowed to each terminal.However, the terminal may perform nulling to the frequency componentscorresponding to the guard band 450 in the basic band unit among thewideband data, thereby preventing interference with the external BSSterminals.

According to another embodiment of the present invention, if thetransmission band is changed from the first band to the second bandduring data transmission, the terminal may transmit the data by settingthe guard band 450 on the basis of the changed second band. That is, ifthe transmission bandwidth is reduced during data transmission, theterminal sets a spectrum mask based on the reduced transmissionbandwidth and transmits the data.

According to another embodiment of the present invention, a multi-userdata transmission using a plurality of subbands in the first band may beperformed. In this case, each subband has a narrower bandwidth than thefirst hand. The plurality of subbands may be contiguous channels, or maybe non-contiguous channels. In addition, each subband may be set to thesame bandwidth, or may be set to a different bandwidth. According to anembodiment of the present invention, a terminal transmits multi-userdata by setting a guard band 450 and a spectrum mask based on eachsubband through which data is transmitted.

FIGS. 14 and 15 illustrate a method of configuring a preamble of anon-legacy packet according to an embodiment of the present invention.More specifically, FIG. 14 illustrates a method of transmitting a legacypreamble (L-preamble) of a non-legacy terminal in a process of amulti-user uplink data transmission. Further, FIG. 15 illustrates amethod of configuring a non-legacy preamble in the process of amulti-user data transmission.

The legacy preamble is decodable at the legacy terminals and includes alegacy short training field (L-STF), a legacy long training field(L-LTF), and a legacy signal field (L-SIG). The non-legacy preamble is afield following the legacy preamble and can be recognized only bynon-legacy terminals (e.g., an 802.11ax wireless LAN terminal). Thenon-legacy preamble may include an HE signal A field (HE-SIG-A), an HEsignal B field (HE-SIG-B), an HE short training field (HE-STF), an HElong training field (HE-LTF), and the like.

The non-legacy wireless LAN packet includes a legacy preamble for legacyterminals and a non-legacy preamble for non-legacy terminals. The legacypreamble and the non-legacy preamble are inserted at the beginning of anon-legacy PHY Service Data Unit (PSDU). Non-legacy wireless LAN systemsmay support 256 FFT while legacy wireless LAN systems support 64 FFT.Thus, at least some of the non-legacy preamble may be composed of 256FFT-based OFDM symbols. When a plurality of non-legacy STAs perform amulti-user uplink data transmission, each STA transmits at least someinformation of a non-legacy preamble through a sub-channel allocated tothe STA. However, since the legacy preamble is transmitted on a 20 MHzchannel basis, a method is required for the STAs assigned to resourceson a sub-channel basis to transmit a legacy preamble in thecorresponding channel.

According to an embodiment of the present invention, as shown in FIG. 14(a), a representative STA selected from a plurality of STAs may transmita legacy preamble 510 on behalf of the plurality of STAs assigned to thesame 20 MHz channel. Various methods can be used to select therepresentative STA among a plurality of STAs. According to anembodiment, a STA having the highest received signal strength indication(RSSI) among a plurality of STAs assigned to the same 20 MHz channel maytransmit a legacy preamble 510 for the multi-user uplink datatransmission. According to another embodiment, a STA assigned to thefirst sub-channel among a plurality of sub-channels allocated within thesame 20 MHz channel may transmit a legacy preamble 510 for themulti-user uplink data transmission.

The representative STA transmits the legacy preamble 510 in units of 20MHz, and then transmits the non-legacy preamble 520 through thesub-channel allocated to the STA. The remaining STAs other than therepresentative STA transmit the non-legacy preamble 520 through thesub-channel allocated to the corresponding STA after the transmission ofthe legacy preamble 510 of the representative STA. The plurality of STAstransmit the non-legacy preamble 520 through allocated sub-channels atthe same time.

According to another embodiment of the present invention, as shown inFIG. 14 (b), a plurality of STAs assigned to the same 20 MHz channel maysimultaneously transmit the legacy preamble 510. In this case, thelegacy preamble 510 transmitted by a plurality of STAs is set to thesame waveform. Each STA transmits the legacy preamble 510 set in thesame waveform in units of 20 MHz, and then transmits the non-legacypreamble 520 through a sub-channel allocated to the corresponding STA.To this end, the AP may transmit information corresponding to the legacypreamble 510 to each STA in the scheduling process. The AP receives thelegacy preamble 510 from at least one STA as common information in unitsof 20 MHz.

FIG. 15 illustrates a method of configuring a non-legacy preambleaccording to an embodiment of the present invention. In the embodimentof FIG. 15 , the same or corresponding parts as those of the embodimentof FIG. 14 described above will be omitted.

FIG. 15 (a) illustrates an embodiment for constructing a non-legacypreamble. Some fields of the non-legacy preamble, for example, theHE-SIG-A 522 may be composed of 64 FFT-based OFDM symbols same as thelegacy preamble 510. According to an embodiment of the presentinvention, the HE-SIG-A 522 of the non-legacy preamble may betransmitted on a 20 MHz channel basis in common. STAs that perform themulti-user uplink data transmission transmit the legacy preamble 510 andthe HE-SIG-A 522 having the same information on a 20 MHz channel basis.That is, the AP receives HE-SIG-A 522 from at least one STA as commoninformation on a 20 MHz channel basis. Also, the STAs transmit theremaining field 524 of the non-legacy preamble through the sub-channelallocated to the corresponding STA. That is, the AP receives theremaining field 524 of the non-legacy preamble as individual informationfor each sub-channel allocated to each STA. In this case, the remainingfields 524 of the non-legacy preamble include HE-STF and HE-LTF.

FIG. 15 (h) illustrates another embodiment constituting the non-legacypreamble. According to another embodiment of the present invention, theHE-SIG-A 522 of the non-legacy preamble may be transmitted on asub-channel basis. STAs that perform the multi-user uplink datatransmission transmit a legacy preamble 510 having the same informationon a 20 MHz channel basis. Also, the STAs may transmit the non-legacypreambles 522 and 524 through a sub-channel allocated to thecorresponding STA. The STA having assigned a plurality of sub-channelsas resources may repeatedly transmit the same HE-SIG-A 522 through eachassigned sub-channel.

Meanwhile, although FIG. 15 illustrates a method of configuring anon-legacy preamble in a situation of the multi-user uplink datatransmission, the method can be applied to the multi-user downlink datatransmission as well. The HE-SIG-A 522 of the non-legacy preambleincludes information necessary to interpret the non-legacy packet. Forexample, the HE-SIG-A 522 may include an indicator indicating whetherthe packet is an uplink packet or a downlink packet. According to theembodiment of the present invention, HE-SIG-A may be duplicated in unitsof 20 MHz when data is transmitted through a wideband channel.

FIG. 16 illustrates a method for performing a multi-user uplinktransmission according to an embodiment of the present invention. In theembodiment of FIG. 16 , the same or corresponding parts to those of theembodiments of FIGS. 9 and 10 described above will be omitted.

The multi-user uplink transmission in a non-legacy wireless LAN systemmay be initiated by a trigger frame. That is, the initialization step(S210) of FIG. 9 may be performed by a transmission of the trigger frameof the AP. STAs that perform the multi-user uplink transmissionsimultaneously transmit uplink data a predetermined IFS after thetransmission of the trigger frame. The trigger frame indicates the startpoint of the multi-user uplink transmission and may indicate informationon the channel or sub-channel allocated to each uplink transmission STA.STAs in which a channel or a sub-channel has been allocated from the APsimultaneously transmit uplink data at the time point designated by theAP. When the multi-user uplink transmission is completed, the APtransmits a multiplexed group ACK in response thereto.

According to an embodiment of the present invention, the trigger framemay include information for NAV setting of the multi-user uplink datatransmission process. When the trigger frame conforms to the legacyframe format, a NAV of legacy terminals can be set based on the durationfield value of the MAC header of the trigger frame. According to afurther embodiment of the present invention, in order to set a NAV forhidden nodes adjacent to uplink transmission STAs, the AP may increasethe coverage of the trigger frame to be more than the transmission rangeof a normal frame. For example, an AP may transmit the trigger framewith increased power than a normal frame. Alternatively, the AP mayapply a robust MCS (Modulation and Coding Scheme) to the trigger frameas compared to a normal frame.

FIG. 17 illustrates a structure of a multiplexed group ACK according toan embodiment of the present invention. According to an embodiment ofthe present invention, the multiplexed group ACK may have a frame formatof a block ACK (BA).

The multiplexed group ACK includes a BA Control field and a BAInformation field and may indicate block ACK information for a pluralityof STAs through at least one of the fields. The block ACK informationfield is set to a variable length and may include a Per TID informationfield, a Block ACK Starting Sequence Control field, and a Block ACKBitmap field. The Per TID information field includes a reserved field(B0 to B11) and a TID Value field (B12 to B15).

According to an embodiment of the present invention, ACK information fora plurality of STAs may be represented by using a reserved field of thePer TID information field. More specifically, the reserved fieldincludes AID information of a recipient STA and an indicator indicatingwhether or not the ACK is a block ACK. For example, the reserved fieldmay be composed of 12 bits (i.e., B0 to B11). A particular bit, forexample, B11, may indicate whether the frame is a block ACK or a normalACK. In addition, some remaining bits of the reserved field, forexample, 11 bits of B0 to B11, may indicate AID information of therecipient STA of the corresponding frame.

The block ACK information field having the above-described configurationmay be repeated for each Traffic ID (TID). Since the block ACKinformation field has a variable length, AIDs for all STAs participatingin the multi-user uplink transmission may be inserted into the block ACKinformation field through the reserved field. For example, the block ACKinformation field is allocated for each STA, and may be repeated by thenumber of recipient STAs. Thus, an AID, a Block ACK Starting SequenceControl field, and a Block ACK Bitmap field for each STA may be includedin the block ACK information field. On the other hand, when theindicator B11 of the reserved field indicates a normal ACK, the BlockACK Starting Sequence Control field and the Block ACK Bitmap field maybe omitted from the block ACK information field.

According to an embodiment of the present invention, informationindicating a BA for a multiple STAs (e.g., a Multi-STA BA) may beincluded in a block ACK control field. More specifically, the block ACKcontrol field includes a Multi-TID field B1, a Compressed Bitmap fieldB2 and a reserved field B3 to B11, and whether the frame is a Multi-STABA is indicated through at least one of the fields. For example, aspecific bit among the reserved field B3 to B11 may be used as a bitindicating the Multi-STA BA.

FIG. 18 illustrates a method of transmitting a multiplexed group ACKaccording to an embodiment of the present invention. In the embodimentof the present invention, the multiplexed group ACK includes a Multi-STABA for a plurality of STAs as described above.

As in the above-described embodiment, uplink data for each channel inthe multi-user uplink transmission may be terminated at the same time.In this case, the AP transmits a multiplexed group ACK on each channelthrough which the multi-user uplink data is transmitted to notify thecompletion of the transmission. However, if the number of STAs assignedto each channel is different as shown in FIG. 18 , at least someinformation of the multiplexed group ACKs transmitted on each channelmay have different lengths. As described above with reference to FIG. 17, the block ACK information field of the multiplexed group ACK has avariable length, and the length of the field may be longer as the numberof assigned STAs increases. Depending on whether the indicator of thereserved field indicates a block ACK, some fields such as a Block ACKStarting Sequence Control field and a Block ACK Bitmap field may beomitted. However, according to the embodiment of the present invention,the L-SIG and the HE-SIG-A may be duplicated as common information inunits of 20 MHz when data is transmitted through a wideband channel.Therefore, the multiplexed group ACKs transmitted on each channel shouldhave the same length based on the value of a PPDU length field includedin the L-SIG.

FIG. 19 illustrates a length alignment method of block ACKs according toan embodiment of the present invention. In an embodiment of the presentinvention, the block ACK includes a multiplexed group ACK and aMulti-STA BA. In the embodiment of FIG. 19 , the same or correspondingparts as those of the embodiment of FIG. 17 described above will beomitted.

The AP transmits a block ACK in response to the multi-user uplink data.The AP may transmit the block ACK to a plurality of STAs using amulti-user downlink transmission. According to an embodiment of thepresent invention, the AP may transmit a block ACK for a correspondingSTA on a channel through which multi-user uplink data is transmitted.

In this case, the amount of ACK information of the block ACK transmittedon each channel may be different. Referring to FIG. 19 , ACK informationof STA1, STA2, STA3 and STA4 is included in the block ACK transmitted onthe first channel, and ACK information of STA5 and STA6 is included inthe block ACK transmitted on the second channel. In addition, ACKinformation of STAT is included in the block ACK transmitted on thethird channel, and ACK information of STA8 and STA9 is included in theblock ACK transmitted on the fourth channel.

According to an embodiment of the present invention, the transmission ofthe block ACK may be terminated at the same time for each channel. Thatis, the AP may set the lengths of block ACKs transmitted on a pluralityof channels to be the same.

According to an embodiment of the present invention, as shown in FIG. 19(a), the AP may perform padding on a block ACK transmitted through atleast one channel to match the termination point of the block ACKtransmissions in each channel. That is, the AP may perform padding onthe block ACKs of the second channel to the fourth channel in referenceto the length of the block ACK of the first channel having the largestamount of ACK information. According to an embodiment, the padding ofthe block ACK may be implemented with zero padding. However, the presentinvention is not limited thereto and the padding may also be implementedwith one padding.

According to another embodiment of the present invention, as shown inFIG. 19 (b), the AP may insert duplicated ACK information into a blockACK transmitted through at least one channel to match the terminationpoint of the block ACK transmissions in each channel. That is, the APmay insert duplicated ACK information into the block ACKs of the secondchannel to the fourth channel in reference to the length of the blockACK of the first channel having the largest amount of ACK information.In this case, the duplicated ACK information includes at least one of aPer TID information field, a Block ACK Starting Sequence Control field,and a Block ACK Bitmap field for each STA.

If the indicator B11 of the reserved field indicates a block ACK, thePer TID information field, the Block ACK Starting Sequence Control fieldand the Block ACK Bitmap field for at least one STA may be inserted induplicate into the block ACK transmitted on the second to fourthchannels. However, if the indicator B11 of the reserved field indicatesa normal ACK, the Block ACK Start Sequence Control field and the BlockACK Bitmap field may be omitted from the block ACK information field.Therefore, the Per TID information field for at least one STA may beinserted in duplicate into the block ACK transmitted through the secondto fourth channels. As described above, the Per TID information field ofthe block ACK information field includes AID information of therecipient STA.

FIG. 20 illustrates a method of frame length alignment by padding in amulti-user simultaneous transmission according to an embodiment of thepresent invention.

According to an embodiment of the present invention, a trigger framethat triggers the multi-user simultaneous transmission may be also bepadded. In the multi-user uplink data transmission and the multi-userdownlink data transmission, a different number of STAs may be assignedto each channel. The trigger frame may include AID information of theSTA assigned to each channel, and the amount of information of thetransmitted trigger frame may be different for each channel.

According to an embodiment of the present invention, a predeterminedpadding may be performed before a Frame Check Sequence (FCS) field ofthe trigger frame. Thus, the transmission of the trigger frame may beterminated at the same time in each channel through which the triggerframe is transmitted. Also, through the padding of the trigger frame,the STAs can acquire additional processing time to participate in themulti-user simultaneous transmission in response to the trigger frame.Meanwhile, according to another embodiment of the present invention, theduplicated AID information may be inserted before the FCS field of thetrigger frame.

As described above, when different numbers of STAs are assigned to eachchannel in the multi-user simultaneous transmission process, the amountof information of the block ACK transmitted in response to themulti-user data may be different for each channel. According to anembodiment of the present invention, padding may be performed on a blockACK of another channel in reference to a length of a block ACK of achannel to which a largest number of STAs are allocated. In this case,the padding may be performed before the FCS field of the block ACK.

FIG. 21 illustrates a method of transmitting a multiplexed block ACKwhen a plurality of channels are used for a multi-user uplinktransmission. In the present invention, the multiplexed block ACK (M-BA)may indicate the above-described multiplexed group ACK.

As described above, the AP may transmit a multiplexed block ACK for acorresponding STA on a channel through which multi-user uplink data istransmitted. Therefore, the length of the multiplexed block ACK variesdepending on the number of STAs assigned to the corresponding channel,the reception state of the multi-user uplink data, and the like.Therefore, at the time when the AP transmits the trigger frame, theactual length of the multiplexed block ACK cannot be predicted.

According to the embodiment of the present invention, the AP may set theTXOP value of the trigger frame by predicting the maximum time requiredfor a multi-user uplink data transmission. The maximum time may be setto a time required for transmitting an M-BA using the block ACK optionto all STAs on the channel through which the largest number of STAs areallocated. Therefore, when the actual multi-user uplink datatransmission is completed, the length of the actual M-BA may bedifferent for each channel depending on the uplink data receptionresult.

If M-BAs of different lengths are transmitted for each channel, accessof other terminals may be allowed an AIFS time after the transmissioncompletion of M-BA on some channels. When the M-BA on the primarychannel is set to be the shortest as in the embodiment of FIG. 21 ,other terminals may perform access to the primary channel. However,since the AP cannot switch its state until the M-BA transmissions onother channels are completed, the transmission attempts of otherterminals may be ignored or the competition of an access attempt of theAP may be disadvantageous.

Therefore, according to the embodiment of the present invention, the APmay set the lengths of multiplexed block ACKs transmitted through aplurality of channels to be the same. To this end, the AP may performpadding on the multiplexed block ACKs transmitted through at least onechannel to match the termination points of the multiplexed block ACKtransmissions in each channel. According to an embodiment, the paddingscheme of IEEE 802.1 lac may be used for the padding of multiplexedblock ACKs.

Meanwhile, the transmission of the multiplexed block ACK may beterminated before the TXOP set in the trigger frame. According to anembodiment, the AP may return the remaining TXOP after the transmissionof the multiplexed block ACK is completed. According to anotherembodiment, the AP may perform additional operations such as a controlframe transmission during the remaining TXOP after the transmission ofthe multiplexed block ACK is completed.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICS s), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

MODE FOR INVENTION

As above, related features have been described in the best mode.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

1-12. (canceled)
 13. A wireless communication terminal, the terminalcomprising: a transceiver; and a processor, wherein the processor isconfigured to: receive trigger frame for soliciting uplink transmissionto multiple terminals, wherein the trigger frame includes a specificfiled for assigning an association identifier (AID) and a frame checksequence (FCS) field, wherein the specific field is set to a specificvalue associated with a padding field, when the trigger frame includethe padding field, wherein the specific value is a value in which eachof a plurality of bits constituting the specific field is repeatedly setto the same value, and wherein the padding field is contained before theFCS field included in the trigger frame, and transmit the response framein response to the trigger frame.
 14. The wireless communicationterminal of claim 13, wherein the padding field is used for processingtime for the terminal to prepare the response frame.
 15. The wirelesscommunication terminal of claim 13, wherein the padding field is used toadjust a length of the trigger frame.
 16. The wireless communicationterminal of claim 13, wherein the specific field is used for allocatingthe AID or padding of the trigger frame according to whether the paddingfield is included in the trigger frame.
 17. The wireless communicationterminal of claim 13, wherein all of the plurality of bits constitutingthe specific field are set to ‘1’.
 18. The wireless communicationterminal of claim 13, wherein the trigger frame is padded by insertingduplicate bit values into the padding field.
 19. A wirelesscommunication method of a wireless communication terminal, comprising:receiving trigger frame for soliciting uplink transmission to multipleterminals, wherein the trigger frame includes a specific filed forassigning an association identifier (AID) and a frame check sequence(FCS) field, wherein the specific field is set to a specific valueassociated with a padding field, when the trigger frame include thepadding field, wherein the specific value is a value in which each of aplurality of bits constituting the specific field is repeatedly set tothe same value, and wherein the padding field is contained before theFCS field included in the trigger frame; and transmitting the responseframe in response to the trigger frame.
 20. The wireless communicationmethod of claim 19, wherein the padding field is used for processingtime for the terminal to prepare the response frame.
 21. The wirelesscommunication method of claim 19, wherein the padding field is used toadjust a length of the trigger frame.
 22. The wireless communicationmethod of claim 19, wherein the specific field is used for allocatingthe AID or padding of the trigger frame according to whether the paddingfield is included in the trigger frame.
 23. The wireless communicationmethod of claim 19, wherein all of the plurality of bits constitutingthe specific field are set to ‘1’.
 24. The wireless communication methodof claim 19, wherein the trigger frame is padded by inserting duplicatebit values into the padding field.